Electrospun nanofiber separator derived from nano-SiO₂-modified polyimide with superior mechanical flexibility for high-performance lithium-ion battery

Nowadays, commercial polypropylene (PP) and polyethylene separators in lithium-ion batteries (LIBs) still remain significant challenges of irreversible deformation, thermal shrinkage or even melting phenomena under external forces and high operating temperature, resulting in short circuit and thermal runaway of the LIBs. Herein, a kind of biphenyl polyimide (PI) nanofiber separator coated with SiO₂ nanoparticles (SiO₂–PI) is prepared via a simple and effective in situ dispersion method coupled with electrospinning technology and used as the separator of LIBs. The combination effect of the three-dimensional network and the extremely high porosity of 92% originating from the electrospinning technology as well as the well-dispersed SiO₂ nanoparticles provides an ultrahigh mechanical flexibility, thermal stability, electrolyte wettability and ionic conductivity of the obtained SiO₂–PI separator compared to the classical PP separator. These superior properties of the SiO₂–PI separator endow the obtained LIBs with much enhanced electrochemical performances. For example, the initial specific discharge capacity of the SiO₂–PI-based LIB is up to 158.4 mAh g⁻¹ at 0.1 C and 125.7 mAh g⁻¹ at 1 C, which can be retained at 90% after 100 cycles. These values, are much better than those of the PP-based LIB, i.e., 156.1 mAh g⁻¹, 100.8 mAh g⁻¹ and 76%, respectively.